In general, a passenger protecting apparatus such as an air bag apparatus is used for protecting a passenger when a vehicle causes a collision. According to US 2004/0243294 A1 (JP-A-2003-54359), an air bag apparatus is constructed of front sensors, a floor sensor, and an electronic control unit. The front sensors are respectively provided to the front right side and the front left side of a side member of the vehicle. The floor sensor is provided to the vicinity of the floor tunnel in the center of the vehicle. The front sensor and the floor sensor respectively detect magnitude of deceleration of the vehicle at each location thereof with respect to backward and forward direction of the vehicle. The electronic control unit activates an airbag in accordance with the magnitude of the deceleration detected using the front sensor and the floor sensor. The electronic control unit stores a determination map for determining activation of the air bag in accordance with the magnitude of the deceleration. The determination map includes a high map, a low map, and a front map.
When floor deceleration, which is detected using the floor sensor, becomes greater than a threshold defined by the high map, the electronic control unit activates the air bag. When the floor deceleration becomes greater than a threshold defined by the low map, and front deceleration, which is detected using the front sensor, becomes greater than a threshold defined by the front map, the electronic control unit activates the air bag. Thus, the air bag is expanded to protect a passenger.
The front sensor is arranged in the front side of the vehicle. Therefore, when the vehicle causes collision, the front sensor may be broken and a wire harness, which connects the front sensor with the electronic control unit, may be disconnected due to the collision. It is impossible to completely protect the front sensor and the wire harness when the vehicle causes collision. Accordingly, when blackout, i.e., disruption arises in a signal transmitted from the front sensor, the front sensor may be determined to be broken, or the wire harness may be determined to be disconnected, due to collision of the vehicle. In this condition, determination in accordance with the front map may be forcibly made, so that the air bag can be activated in accordance with the determinations, which is forcibly made, and the determination based on the low map, even when the front sensor is broken or the wire harness is disconnected due to collision of the vehicle.
However, blackout of the signal transmitted from the front sensor is not necessarily caused by collision of the vehicle. The signal may cause blackout due to malfunctions of the front sensor and an input device of the electronic control unit. For example, when water intrudes into the vehicle, and components of the air bag apparatus are excessively exposed to water, each of the front sensor and the input device of the electronic control unit may cause a malfunction. In addition, the floor deceleration may gradually vary due to leakage caused by intruding water.
When each of the front sensor and the input device of the electronic control unit causes a malfunction, and blackout arises in the transmittance of the signal, determination in accordance with the front map may be forcibly made. In this case, when the floor deceleration gradually varies and becomes greater than the threshold defined by the low map, the air bag may be activated even the vehicle does not cause collision.
Another structure may be constructed by combining a safing determination in accordance with the front deceleration and low and high speed collision determination in accordance with the floor deceleration. In this structure, when the front deceleration becomes greater than a safing threshold, and the floor deceleration becomes greater than a low speed collision threshold, the electronic control unit may activate the air bag. Alternatively, when the front deceleration becomes greater than a safing threshold, and the floor deceleration becomes greater than a high speed collision threshold, the electronic control unit may activate the air bag.
The floor deceleration when the vehicle cause low speed collision is less than the floor deceleration when the vehicle cause high speed collision. However, the floor deceleration of the low speed collision may gradually vary during a long period. When each of the front sensor and the input device of the electronic control unit causes a malfunction, and blackout arises in the transmittance of the signal, the sating determination may be forcibly made. In this condition, when the signal output from the floor sensor causes a drift, the floor deceleration effected by the drift becomes similar to the floor deceleration of the low speed collision. Accordingly, the floor deceleration may become greater than the low speed collision threshold, and the air bag may be activated even the vehicle does not cause a collision.